Thermal switch

ABSTRACT

A thermal switch comprises a base member which carries portions of an electrical alarm circuit and switch contacts therefor, and a removable cap which carries a heat-sensitive element and means for operating said switch contacts in response to ambient heat.

United States Patent Matto 5] Mar. 14, 1972 [54] THERMAL SWITCH FOREIGN PATENTS OR APPLICATIONS 1,104,994 6/1955 France ..337/ll3 640,318 7/1950 GreatBritain ..337/1l3 Broadley et a1. ..337/1 12 X Primary Examiner-Bramard A. Gilheany Assistant Examiner-F. E. Bell Attorney-Robert A. Green [5 7] ABSTRACT A thermal switch comprises a base member which carries portions of an electrical alarm circuit and switch contacts therefor, and a removable cap which carries a heat-sensitive element and means for operating said switch contacts in response to ambient heat.

6 Claims, 4 Drawing Figures \E 1 F 1 E c/go PATENTEDMAR 14 1972 3,54

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INVENTOR. V ictor G. Mutto ATTORNEY THERMAL SWITCH BACKGROUND OF THE INVENTION Thermal switches of different types are known in the art; however, these known switches are not completely satisfactory. In general, these switches have relatively small heat collector surfaces, and some have relatively cumbersome, inefficient platelike attachments to increase their effective areas. Such attachments require a separate mounting operation which adds to cost, and they get in the way of the installer. Esthetically, such devices having attachments are relatively unsightly and, in addition, all the mounting screws show. In addition, prior art switches require that the wires be attached to the switch before the switch is mounted on the ceiling or the like. This is always a relatively difficult and clumsy operation which is made even more complicated when several switches are connected together in series-parallel, as is commonly done. In general, most prior art switches are relatively complicated structurally, and, in all, if the heat-sensing element becomes inoperative or it is desired to change the temperature rating, the entire switch must be'replaced.

The present invention provides a relatively simple thermal switch which has a large-area heat collector, and it is constructed so that, if the heat-sensing element becomes inoperative, it can be replaced with ease. In addition, all mounting screws are hidden, and the device has a simple, esthetically attractive housing, and it is constructed with a minimum number of parts so that assembly and installation are simple operations.

SUMMARY OF THE INVENTION Briefly, the invention comprises a thermal switch having a base which includes a portion of the signal circuitry and a removable cap which includes a heat-sensitive element and means for closing the signal circuit in response to heat.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective exploded view of portions of the invention;

FIG. 2 is a perspective view of a portion of the apparatus shown in FIG. I with the parts assembled;

FIG. 3 is an elevational view, partly in section, of the invention; and

FIG. 4 is a sectional elevational view of a portion of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A thermal switch embodying the invention includes a generally cup-shaped base 20 of insulating material which is divided into two compartments 30 and 40 by a wall 50. The upper end of the outer surface of wall 60 of the base 20 has an annular indentation 62, for a purpose to be described. The wall 60 rises suitably above the inner surface 63 of the base. The base has at least two through-holes 64 and 66 oriented on a diameter, one in each compartment and preferably near wall 60, which are adapted to receive screws 67, by means of which the base can be secured to the ceiling, or other suitable location, in a room to be protected. The base 20 is also provided with two through-holes 68 and 70 positioned side by side, one in each compartment, adjacent to dividing wall 50 and to outside wall 60. Holes 68 and 70 are used to bring circuit wires into the base for connection to terminals to be described. A similar through-hole 72 is provided in base 20 aligned on a diameter with hole 68 and positioned at the other end of the diameter adjacent to wall 60 and in compartment 30. A similar hole 74 is provided in compartment 40 aligned with hole 70. Holes 72 and 74 are also used to pass wires into or out of the housing where switches are connected in series-parallel, as is well known in the art.

Between holes 68 and 72 and aligned therewith are, in order, a cylindrical depression 76, a through hole 78, and a cylindrical depression 80. Similarly, between holes 70 and 74 and aligned therewith are, in order, a cylindrical depression 82, a through hole 84, and a cylindrical depression 86. The base also includes an insulating split-wall tubular member 88 in chamber 30 adjacent to hole 78 and a similar insulating split-wall tubular member 89 in chamber 40 adjacent to hole 84. The base and its holes and members 88 and 89 are preferably molded in one piece.

The base 20 carries a first terminal strip 90 which comprises a flat, somewhat elongated metal strip having two spacedapart threaded holes and and a mounting hole between them. The strip 90 is secured to the surface 63 of base 20 by means of a rivet or the like inserted in hole 120 in plate 90 and hole 78 in base 20 which is aligned therewith. With strip 90 thus secured, threaded hole 100 overlays and is aligned with depression 76 in base 20, and threaded hole 110 overlays and is aligned with depression 80 in base 20.

A screw is adapted to be threaded into hole 100 in plate 90 and into depression 76, and it is used to secure to plate 90 a first wire which enters through-hole 68. A first L-shaped metal terminal 160, including a horizontal ring having hole and a vertical split cylinder coupled together by a tab 192, has the ring portion positioned between surface 63 and the strip member 90, and it is secured in place by the rivet 130 which passes through the hole 180 in the ring 170. The parts are arranged so that, when the L-shaped terminal member 160 is secured in place, cylinder 190 is inserted and positioned in split-wall insulating cylinder 88, with connecting portion 192 extending through the open wall portion of cylinder 88.

A threaded screw 200 is adapted to be threaded into hole 110 in strip member 90 and into depression 80 in base 20. Screw 200 may be used to secure a wire (not shown) to strip 90 for series connection to another switch (not shown) or for any other purpose.

Identical structural members, including a terminal strip 90, L-shaped terminal 160', screws and wires, etc., are mounted in chamber 40, with corresponding parts carrying the same reference numeral primed.

The thermal switch 10 also includes a cover member or cap 240 which is a large-area heat collector and is of metal. The cover is generally cylindrical, and it includes a first central dish-shaped portion 250 which is concave when viewed from the inner surface. Adjacent to the first central dish-shaped portion 250 is a tapered annular wall 260, a third vertical wall 270, a fourth annular tapered wall 280, and a fifth vertical wall 290.

A bimetallic disk 300 is seated inside the cap on the inner surface 310 of the central portion 250, and a thin, flat insulating disk 320, preferably of Teflon, is seated on the bimetallic disk. The insulating disk 320 is preferably color-coded to represent the operating temperature of the bimetallic disk. The bimetallic disk is concave or convex, depending on whether the switch is to be normally open or normally closed, but preferably its curvature is the same as that of central portions 250.

An insulating support plate 330 having top surface 334 and bottom surface 336 is seated in the ring defined by the first vertical wall 270 and makes a tight fit therewith. The top surface of the plate 330 has an elongated depression 340 extending along a diameter, and through-holes 344 and 346 are pro vided therein near the ends of the depression. Two semicircular ridges or walls 348 and 350 rise from the top surface 334 and are positioned so that they bear against the insulating disk 320 and thus against the bimetallic disk 300 at their peripheries to hold the two disks securely in place in the central region 250 of the cap.

The plate 330 carries two electrical contact pins 354 and 356 which are secured in place by means of ribs 358 and 360 which bear against the bottom surface 336 and have their upper ends 362 and 364 rolled over to bear against the top surface of the disk 330 in the aperture 340.

In addition, a resilient metal contact strip 370 is secured at one end by the turned-over upper end 362 of pin 354 which is positioned in a hole in the strip 370. The contact strip 370 is of such width that it is seated in, and flts snugly in, the depression 340 and is prevented from rotating laterally thereby.

The metal contact arm 370 carries at about the center of its top surface a nodule 380 which bears against the insulating plate 320, and, at its free end, it has a metallic contact nodule 390 which is positioned to contact a metallic insert button 37] positioned in end 364 of pin 356 and making a tight fit therewith. Nodule 390 contacts button 371 when the bimetallic element is actuated and flexed away from the inner surface of cap 240 exposed to heat. When nodule 390 contact button 371, a circuit is completed between the pins 354 and 356. This represents the normally open switch arrangement. In the normally closed arrangement, the bimetallic disk is reversed, and it holds contact arm 370 closed against the contact 371 when it is energized by heat.

The contact pins 354 and 356, or the portions thereof which extend away from the bottom surface 336 of the plate 330, are positioned and shaped so that each enters and makes contact with one of the metallic cylinders 110 and 110', as shown in FIG. 1, when the cap 240 is coupled to the base. The pins are large enough and strong enough and the cylinders 190, 190 gn'p securely enough to rigidly secure the cap to the base as substantially the sole coupling means. The wall 290 of the cap does not make contact with the wall of the base, but is slightly spaced therefrom as shown at 291, and thus provides no gripping action between the cap and the base. This arrangement insures that heat will not be coupled from the cap to the base.

in mounting the switch 10, the necessary wires 150 and 150', which come from a remote signal circuit, are fed in through holes 68 and 70 or through a broken-out portion of the indented or narrowed wall 62 in base 20, and they are secured to screws 140 and 140'. The base is then screwed to the ceiling with screws 67 inserted in holes 64 and 66. If desired, the base may first be secured to the ceiling, and then the wires 150, 150' may be secured to the screws 140, 140'. Now, the selected cap 240 having the proper bimetallic disk 300 and carrying the other elements described above, is coupled to the base to which it is secured by means of pins 354 and 356. The pins 354 and 356 are inserted into, and are securely held by, cylinders 190 and 190' which themselves are held within cylinders 88 and 89. The latter cylinders prevent the metal cylinders from becoming enlarged in use. If at any time it is desired to change the bimetallic'element, the cap is removed, and the new cap and new element are attached. If necessary, the cap can be removed by a screwdriver inserted into notch 400 in the outer wall of the base.

The ease of operation and the simplicity of construction of the switch of the invention are clear from the foregoing description of the invention.

in actual operation of the switch itself, the large-size metal cap 240 serves as an efficient heat collector which readily couples heat to the bimetallic disk 300. When the disk is heated sufl'iciently, its central portion flexes as its periphery is supported by rings 348 and 350 of disk 330. When the bimetallic disk flexes, it pushes nodule 380 and contact strip 370 toward plate 330, and its end nodule 390 touches contact 371. This completes a circuit between pins 354 and 356, through cylinders 190, 190', strips 90 and 90', and wires 150 and 150' to the alarm circuit at some remote location.

What is claimed is:

1. A thermal switch for connection in an alarm signaling system comprising a cylindrical base member of insulating material having an outer curved surface, a lower surface and an upper surface, said base member adapted to be mounted on a support surface with its lower surface being positioned adjacent to said support surface and with its upper surface facing away from said support surface and accessible to a user of said switch,

a pair of tubular metallic contacts secured to said upper surface of said base member and having secured thereto wires from said signaling system,

a metallic cap member comprising a large-area curved center heat-absorbing portion and a cylindrical side wall secured thereto,

a bimetallic disk positioned within said cap member in contact with said curved center portion of said cap member, an insulating disk adjacent to and in contact with said bimetallic disk,

an insulating plate carrying a pair of contact pins which are inserted in said tubular metallic contacts and are in tight mechanical engagement therewith,

a metallic contact strip having one end secured to one of said contact pins and having its other end spaced from but adapted to be moved into contact with said second contact pin to close the electrical circuit between the two wires secured to said tubular contacts, I

said metallic contact strip being in contact with said insulating disk, movement of said bimetallic disk in response to heat causing said insulating disk to move said metallic contact strip into contact with said second contact pin to complete said circuit,

said cylindrical side wall of said cap member encircling a portion of said outer curved surface of said base member but spaced therefrom whereby no heat is conducted thereto and all heat received by said cap member is conducted to said bimetallic disk.

2. A thermal switch for connection in an alarm signaling system comprising a cylindrical base member of insulating material including a horizontal wall and-an outer curved wall, said horizontal wall having a lower surface and an upper surface, said base member being adapted to be mounted on a support surface with its lower surface being positioned adjacent to said support surface and with its upper surface facing away from said support surface and accessible to a user of said switch,

said horizontal wall of said base member having a vertical divider wall rising from its upper surface which separates said base member into two compartments,

said horizontal wall of said base member being provided with a plurality of holes which extend therethrough, some of said holes being used for receiving means for securing said base member to said support surface, others of said holes including one in each of said compartments receiving wires which are connected to said signaling system,

a pair of metallic plates secured, one in each compartment, to said upper surface of said horizontal wall, each plate being in electrical contact with a female contact member secured between said plate and said upper surface of said horizontal wall of said basemembets, each plate having means for connecting to one of said wires of said signaling system,

mating cap member adapted to mate with said base member and including a large-area center plate portion and a cylindrical side wall secured thereto and depending therefrom, said center plate portion having an inner surface,

an insulating plate having a lower surface and an upper surface, the upper surface having a pair of aligned slots,

a metallic contact strip having one end secured in one of said slots by means of a male contact pin which extends through said insulating plate into one of said female contact members,

a second male contact pin sec$red to said insulating plate and positioned in the other of said slots and extending through said insulating plate into the other female contact member, said metallic contact strip having a second end normally spaced from but adapted to contact said second male contact to close the electrical circuit between the two wires secured to said female contact members,

a pair of curved support ridges spaced apart and oriented along the periphery of said upper surface of said insulating plate,

an insulating disk seated on said support ridges in contact with said metallic contact strips, and

a thermally sensitive bimetallic disk seated on said insulating disk between said insulating disk and said inner surface of said large-area center plate portion of said cap member and in contact therewith to conduct heat therefrom whereby movement of said bimetallic disk in response to heat can force said contact strip into contact with said second male contact pin to complete said circuit,

said cylindrical side wall of said cap member encircling a portion of said outer curved surface of said base member but spaced therefrom whereby no heat is conducted thereto and all heat received by said cap member is conducted to said bimetallic disk.

3. The switch defined in claim 1 wherein said insulating plate carries a guide depression for receiving said metallic contact strip.

4. The switch defined in claim 1 wherein said insulatingplate includes a top surface having a pair of curved ridges on which said insulating disk seats.

5. The switch defined in claim 1 wherein said base member includes a plurality of through-holes and a pair of metallic contact plates secured to ones of said through-holes and adapted to have wires secured thereto which are fed into said base member through others of said through-holes, each of said contact plates carrying one of said tubular contact members.

6. The switch defined in claim 5 wherein said metallic contact plates carry screws by means of which said wires are secured thereto. 

1. A thermal switch for connection in an alarm signaling system comprising a cylindrical base member of insulating material having an outer curved surface, a lower surface and an upper surface, said base member adapted to be mounted on a support surface with its lower surface being positioned adjacent to said support surface and with its upper surface facing away from said support surface and accessible to a user of said switch, a pair of tubular metallic contacts secured to said upper surface of said base member and having secured thereto wires from said signaling system, a metallic cap member comprising a large-area curved center heat-absorbing portion and a cylindrical side wall secured thereto, a bimetallic disk positioned within said cap member in contact with said curved center portion of said cap member, an insulating disk adjacent to and in contact with said bimetallic disk, an insulating plate carrying a pair of contact pins which are inserted in said tubular metallic contacts and are in tight mechanical engagement therewith, a metallic contact strip having one end secured to one of said contact pins and having its other end spaced from but adapted to be moved into contact with said second contact pin to close the electrical circuit between the two wires secured to said tubular contacts, said metallic contact strip being in contact with said insulating disk, movement of said bimetallic disk in response to heat causing said insulating disk to move said metallic contact strip into contact with said second contact pin to complete said circuit, said cylindrical side wall of said cap member encircling a portion of said outer curved surface of said base member but spaced therefrom whereby no heat is conducted thereto and all heat received by said cap member is conducted to said bimetallic disk.
 2. A thermal switch for connection in an alarm signaling system comprising a cylindrical base member of insulating material including a horizontal wall and an outer curved wall, said horizontal wall having a lower surface and an upper surface, said base member being adapted to be mounted on a support surface with its lower surface being positioned adjacent to said support surface and with its upper surface facing away from said support surface and accessible to a user of said switch, said horizontal wall of said base member having a vertical divider wall rising from its upper surface which separates said base member into two compartments, said horizontal wall of said base member being provided with a plurality of holes which extend therethrough, some of said holes being used for receiving means for securing said base member to said support surface, others of said holes including one in each of said compartments receiving wires which are connected to said signaling system, a pair of metallic plates secured, one in each compartment, to said upper surface of said horizontal wall, each plate being in electrical contact with a female contact member secured between said plate and said upper surface of said horizontal wall of said base members, each plate having means for connecting to one of said wires of said signaling system, a mating cap member adapted to mate with said base member and including a large-area center plate portion and a cylindrical side wall secured thereto and depending therefrom, said center plate portion having an inner surface, an insulating plate having a lower surface and an upper surface, the upper surface having a pair of aligned slots, a metallic contact strip having one end secured in one of said slots by means of a male contact pIn which extends through said insulating plate into one of said female contact members, a second male contact pin secured to said insulating plate and positioned in the other of said slots and extending through said insulating plate into the other female contact member, said metallic contact strip having a second end normally spaced from but adapted to contact said second male contact to close the electrical circuit between the two wires secured to said female contact members, a pair of curved support ridges spaced apart and oriented along the periphery of said upper surface of said insulating plate, an insulating disk seated on said support ridges in contact with said metallic contact strips, and a thermally sensitive bimetallic disk seated on said insulating disk between said insulating disk and said inner surface of said large-area center plate portion of said cap member and in contact therewith to conduct heat therefrom whereby movement of said bimetallic disk in response to heat can force said contact strip into contact with said second male contact pin to complete said circuit, said cylindrical side wall of said cap member encircling a portion of said outer curved surface of said base member but spaced therefrom whereby no heat is conducted thereto and all heat received by said cap member is conducted to said bimetallic disk.
 3. The switch defined in claim 1 wherein said insulating plate carries a guide depression for receiving said metallic contact strip.
 4. The switch defined in claim 1 wherein said insulating plate includes a top surface having a pair of curved ridges on which said insulating disk seats.
 5. The switch defined in claim 1 wherein said base member includes a plurality of through-holes and a pair of metallic contact plates secured to ones of said through-holes and adapted to have wires secured thereto which are fed into said base member through others of said through-holes, each of said contact plates carrying one of said tubular contact members.
 6. The switch defined in claim 5 wherein said metallic contact plates carry screws by means of which said wires are secured thereto. 